In the cervical spine, the average cervical disc is approximately 5–9 mm tall when healthy in an adult of normal stature. Presently, the screws for use in fixating into the cervical vertebral bodies are generally of a diameter of 4–5 mm each and have enlarged head portions for retaining them in the fixation device. Thus, these screws when placed in opposition and vertically aligned would have a combined height that exceeds the height of almost all cervical discs.
Implants of the related art have extended the height of the trailing end of the implant to make it taller than the disc space. An example of this is a flanged implant. The flanged implant makes it possible to place screws so that they can be vertically aligned and have sufficient structure of the implant to retain them. The flanged portion of the implant extends outside of the disc space.
In known interbody spinal fusion implants there have been problems with loosening and backing out of screws into the patient's throat area. These occurrences generally require further surgical procedures to replace the implants and screws entirely, and to repair any damage that may have been caused.
There is a need for an implant having a locking mechanism that can be easily and reliably locked in place to prevent the loosening of and backing out of the bone screws used to attach the implant to the vertebrae in the anterior aspect of the cervical, thoracic, and lumbar spine.